1. Field of the Invention
The present invention relates to a flat panel image display device which uses an electron source.
2. Description of the Related Art
In recent years, a so-called flat panel display attracts attention as an image display device instead of a large and heavy cathode-ray tube. In particular, a liquid crystal display is actively researched and developed. However, it remains as a problem that a view angle is narrow and there is persistence of vision.
On the other hand, a self-emitting flat panel display which displays an image through fluorescence by irradiating an electron beam emitted from an electron source to a fluorescent member is actively researched and developed. As compared with the liquid crystal display, the self-emitting flat panel display can acquire a light image and a wide view angle, and does not remain persistence of vision. For this reason, the self-emitting flat panel display is expected to take the place of the liquid crystal display, in terms of requests of a large-sized screen and a high-definition image.
In regard to the self-emitting flat panel display, Japanese Patent Application Laid-Open No. H03-261024 discloses a flat panel image display device in which electron emission elements for emitting electron beams are disposed within a vacuum panel located between a face plate and a rear plate. In Japanese Patent Application Laid-Open No. H03-261024, the flat panel image display device, which uses a surface-conduction electron emission element as the electron emission element, accelerates the emitted electron beam, irradiates the accelerated electron beam to a fluorescent member, causes fluorescence of the fluorescent member, and thus displays an image.
FIG. 8 is a schematic cross section diagram illustrating a face plate of such an image display device. As illustrated in FIG. 8, the face plate includes a glass substrate 1007, a fluorescent member 1008, a metal back 1009, and a black conductive member (black matrix) 1010. The internal pressure of the flat panel image display device which accelerates and irradiates the electron beam to the fluorescent member 1008 so as to display an image is maintained to a vacuum of 10−6 torr or less. Here, to maintain vacuum is important with the objective of a time-dependent change of luminance, occurrence of luminance variation, and the like. In this connection, Japanese Patent Application Laid-Open No. 09-082245 discloses a flat panel image display device in which a metal back has a getter material.
The reason why the metal back 1009 like this has a getter material is as follows. That is, in the image display device which uses the electron source, since it is impossible to avoid generating gas from an image display member such as the fluorescent member 1008 or the like which is impacted by high-energy electron, it is feared that the generated gas affects a characteristic because the generated gas adsorbs to an electron emission unit of the electron source. Therefore, to sufficiently adsorb such gas, the metal back 1009 provided within an image display range is constituted to have the getter material.
On the occasion when the high-energy electrons bombard and penetrate into the fluorescent member 1008, some of the electrons are scattered backward by the metal back 1009 and the fluorescent member 1008. Then, the backward scattered electrons are accelerated through an electric field, and the accelerated electrons again bombard and penetrate into the metal back 1009 and the fluorescent member 1008 located nearby. Consequently, a phenomenon called halation that fluorescence of the fluorescent member 1008 of a pixel not driven occurs. Further, if the metal back 1009 has the getter material, it is contemplated that a percentage of the electrons scattered backward increases. This is because the material to be used as the getter material includes the element heavier than aluminum to be ordinarily used as the metal back, and thus a backscattering coefficient increases.
As a countermeasure for the halation, Japanese Patent Application Laid-Open No. H11-250839 discloses an image display device in which a third electrode is provided between a rear plate and a face plate. However, it is feared that this kind of third electrode complicates the constitution of the flat panel display and thus increases manufacturing costs.
In the flat panel image display device, as described above, some of the electron beams irradiated to the metal back 1009 are scattered backward. If the metal back 1009 has the getter material, since a mean atomic number of the elements included in the metal back is larger than that of aluminum used as the metal back 1009, the electrons scattered backward increase. Then, the electrons scattered backward are accelerated through the electric field, and the accelerated electrons again bombard and penetrate into the fluorescent member 1008. Here, if an amount of the electrons bombarded and penetrated again is large, the halation occurs, thereby preventing a contrast on the flat panel display.